01 - Preheat oven to 350°F. Lightly grease a 9x13-inch baking dish and set aside.
02 - In a large mixing bowl, combine cake mix, eggs, milk, vegetable oil, and vanilla extract. Beat with a mixer on medium speed for about 2 minutes, until batter is smooth. Pour into prepared baking dish and smooth surface.
03 - Bake for 25 to 30 minutes, or until a toothpick inserted in the center comes out clean.
04 - While cake bakes, mix brown sugar and ground cinnamon in a small bowl. Stir in melted butter until a thick paste forms.
05 - Remove cake from oven when done. Immediately use the handle of a wooden spoon to poke holes evenly over the surface, about 1 inch apart.
06 - Spoon or drizzle cinnamon filling over the warm cake, letting it seep into the holes. Allow cake to cool completely.
07 - In a clean bowl, beat together cream cheese and softened butter until smooth and fluffy. Add powdered sugar, milk, and vanilla extract. Mix until creamy and spreadable.
08 - Spread cream cheese frosting evenly over the cooled cake. Cut into portions and serve.